Finding and fixing the leak.There was no obvious hole for water to enter the aft compartment but the fittings were a possibility. To find out, we hoisted the boat up vertically over a beam in the workshop with main sheet tackle and then half filled the compartment and the drain pipe with water. The drain pipe level did not change but a drip appeared alongside but not as a part of the bung fitting. The leak was in the fillet between the bottom and plank one on the right hand side. On close inspection and a photo from underneath, there was a very fine gap there. The feathered leak investigator confirmed that there was water on the floor!
A second leak appeared to be in between the transom and the doubler. Once again due to a very small gap in the fillet. Who know what the exact flow path was for this one but it was unlikely to be a problem once plugged.
The gap near the bottom was drilled and filled with epoxy; tested again and proven to be fixed.